Photovoltaic solar cells are used to generate electricity from impinging radiation such as solar radiation. Solar cells are typically formed from semiconductors such as silicon, amorphous silicon, cadmium telluride, gallium arsenide and copper indium diselinide. When subjected to impinging radiation, cells comprised of the above semiconductor materials generate an electric current.
One problem with semiconductor solar cells is that the materials comprising the solar cells are typically expensive. As a result, it is difficult to generate electricity with solar cells which is competitively priced with electricity generated by other means, such as hydroelectric power or fossil-fuel combustion. One approach to reducing the costs of semiconductor solar cells has been to make the cells extremely thin, thereby reducing the amount of material required to form each cell. Another method for improving the efficiency of semiconductor solar cells has been to use refractive lenses to focus radiation on the cell, thereby reducing the cell surface area required to receive a given amount of radiation. Such a method and associated device are disclosed in U.S. Pat. No. 5,437,736 to Cole.
One drawback with the conventional methods and devices described above is that the lenses used to focus incoming radiation are typically bulky and nonuniform, resulting in solar cell assemblies which are difficult to handle and which collect dirt and other debris, thereby reducing the efficiency of the solar cells. A further disadvantage of the devices described above is that separate semiconductor solar cells must be electrically coupled to generate electrical current sufficient for typical applications. Electrically coupling the separate solar cells requires the use of additional materials and process steps, thereby increasing the cost of the solar cell assembly.
One approach to addressing the foregoing drawbacks has been to use reflection rather than refraction to direct incident radiation toward the solar cells. U.S. Pat. No. 5,288,337, to Mitchell, discloses a photovoltaic module having a concave lower surface which directs radiation by total internal reflection toward adjacent solar cells. U.S. Pat. No. 4,235,643, to Amick and U.S. Pat. No. 4,313,023, to Stephens, disclose facets which direct radiation by total internal reflection toward an array of circular solar cells. U.S. Pat. No. 4,162,928, to Shepard, Jr., discloses a plate having a regular pattern of uniform indentations which reflect radiation toward a solar cell. U.S. Pat. No. 3,973,994 to Redfield discloses a solar cell having a grooved lower surface which reflects radiation by total internal reflection back and forth between upper and lower surfaces of the solar cell. One drawback of the foregoing devices and methods is that they do not efficiently collect incident radiation and direct the radiation to solar cells. Accordingly, the foregoing methods and devices require a relatively large solar cell surface area to receive a given amount of incident radiation.